Preparation of olefins by particulate coal carbonization



Dec. 23, 1952 A; J. WELLS 2,623,011

PREPARATION OF OLEFINS BY PARTICULATE COAL CARBONIZATION Filed Nov. 30,1946 E 1 3 H 0 q .3 M S E 17-- a g g :2 Q I g 4 3: i 8 4 I! a if.PRflflVCT 6455s I .4 INVENTOR.

Adoizzmm J Wells Patented Dec. 23, 1952 PREPARATION OF OLEFINS BYPARTICU- LATE COAL CARBONIZATION Adoniram J. Wells, Wilmington, Del.,assignor to E. I. du Pont de Nemours 8; Company, Wilmington, DeL, acorporation of Delaware Application November 30, 1946, Serial No.713,374

1 Claim.

This invention relates to an improved process for the preparation ofunsaturated hydrocarbons, and more particularly, the preparation ofethyl ene by the carbonization of coal.

For a number of years an eifort has been made, in the preparation ofilluminating gas by the coking of coal, to provide a high percentage ofilluminants and of the illuminants the olefins are the most effective.Attempts were made to increase the illuminants in coke-oven gas but, duein no small measure to the time lag in heating the coal to carbonizationtemperatures and long-drawn out temperature cycles inherent in suchprocesses, rewards were meager. Furthermore, the difficulties of heattransfer have limited gas production, because of the wide temperaturedifference often existing in the coke ovens. At any one time thetemperature gradients through the carbonizing chamber are quite sharp, atypical condition being that the temperature of the fully coked materialnear the heating wall will be about 1000" 0., while the uncoked coal inthe center will be about 100 C. Inasmuch as the production of gas fromcoal is, by and large, a chemical process and as chemical processes evenof the simpler types require careful and accuratetemperature control forthe production of maximum yields of a given product, it follows thatmodifications of coke-oven technique would not be expected to realizethe maximum yields of gas from coal, with no expectation of directingthe course of the operation to give maximum yields of particularproducts such as olefins.

An object of the present invention is to provide an improved process forthe preparation of olefins by the carbonization of carbonaceousmaterials. Yet another object is to provide a process for thecarbonization of coal in particulate form, whereby the optimumtemperatures for olefin production are realized. A further object is toprovide a process for the coking of powdered coal, wherein high gasproduction to olefins is realized by coking the coal from the fluidizedstate. Another object is to provide a process for coking powdered coal,wherein uninterrupted flow of the coal and coke through the coking zoneis maintained. Other objects and advantages of the invention willhereinafter, appear.

In its broader aspects the invention involves pulverizing coal or othersolid carbonaceous material, such as peat, oil shale, and the like, andwhile dispersed in a fluid medium, subjecting it to high-temperaturecarbonization. In counterdistinction to coke-oven operation, wherein alarge mass of coal is externally heated, requiring a long time to raisethe temperature of the mass Cl. 202l7) to carbonization temperatures,the process of the instant case substantially instantaneously brings thecoal to the optimum temperature for carbonization. Research has shownthat it is necessary, in order to reach the objective of maximum olefinyields from coal, to reduce to a minimum the time the olefin is atcoking or carbonization temperature. With such requirements, coke ovenswere obviously unsuited for maximum olefin production. The process ofthe instant case permits accurate reaction time and temperaturecontrols, thereby making it possible to realize the objective.

By mass spectrometric analysis it has been found, that when carbonizingcoal of smallparticle size, the maximum amounts of olefins are evolvedat temperatures below 1000 C. If the desired olefin is ethylene,temperatures between 800 and 950 C. are best, with a preferred rangebetween 850 and 900 C. If propylene is the desired olefin, the optimumrange is between 700 and 850 C. while if acetylene is the desiredunsaturate, high temperatures are called for, viz. 900 to 1200 C.

In addition to controlled temperature for carbonization, the amount ofolefin or acetylene recovered is determined also by the time they are inthe carbonization zone at temperature. No matter what method of heatingis employed, the unsaturated product gases should be removed from thehot carbonization zone in less than 3 seconds after separation from thecoal. If an externally fired reaction zone is used, the time should bewithin 0.2 and 1.0 second; if a condensable gas is used to provide theheat, the time should range between 0.2 to 2.0 seconds; and, if aboiling bed is used, a time between 0.5 and 3.0 seconds.

There is a third variable which must be controlled to realize thegreatest evolution of the unsaturated hydrocarbons from coal during itscarbonization and that is the particle size of the coal beingcarbonized. If the externally fired reaction zone is used, describedbelow, a 20-mesh size (1. e. a coal that will all pass through a screenhaving 20 holes per linear inch) is the largest that will give optimumproduct yields, with the best yields with a size of about mesh. Whenusing a heating condensable fluid, sizes between 50 and 100 mesh may beused but, preferably, a 100-mesh size or smaller; while with a boilingbed zone, sizes of 100 mesh or smaller are preferred.

The powdered coal may be heated by any suitable means, the coal being,e. g. dropped by gravity through the center of an externally fired tubewhich may or may not also contain a condensable or non-condensable gasthat may flow cocurrent with or countercurrent to the flow of coal, thegas sweeping out the unsaturates formed. Alternatively, the boiling bedtechnique may be used, i. e. the powdered coal is carbonized in aboiling bed, the boiling being supplied by, for example, theintroduction into the bed of a condensable or non-condensable gas, whichmay or may not supply the necessary heat to provide adequatecarbonization. Other methods of heating the tubular reactor or boilingbed reaction will readily suggest themselves to those skilled in theart. Examples of satisfactory methods include external heating; internalheating by sensible heat of a highly heated condensable ornon-condensable gas; internal firing, supplied by partial combustion ofthe coal or by partial combustion of a combustable gas used, forexample, to fiuidize the coal; hot coke heating, whereby the hot coke ismixed in the carbonizer with the powdered coal or is passed directlyinto the boiling bed of a carbonization vessel, or any other suitablemethod may be employed.

The accompanying diagrammatic sketch illustrates one method of operatingthe process, wherein exceptionally high yields of ethylene can beobtained. Figure 1 is a plan view of apparatus which may be employed incarrying out the process of the invention and Figure 2, a sideelevation,more in detail of the apparatus of Figure l. The coal is passed into asuitable crusher i, such as a ball mill screening unit, wherein it ispulverized, and screened to give a powdered coal of the optimum particlesize. From crusher I the coal is dropped into hopper 2 from which itflows by gravity or through a vibrating feeder, into pipe 3 from whichit is blown by air from blower 3 through pipe 5 into a cyclone dustseparator 6 from which the coal particles drop into the stand pipe 1. Inthis pipe the coal particles are in a free-flowing state and duringoperation or" the process the pipe is maintained substantially filled bycontinuous addition thereto as coal is removed from its base. From thejacketed stand pipe I, which provides a static head similar to ahydraulic head, the coal is fed by means of the vibratory tubular feeder8, which is jacketed with steam to prevent condensation and maintain thecoal particles in a dry state, through aperture 9 into the pipe [0. Astream of low-pressure steam 1.0 to p. s. i. passes through the fallingparticles from aperture 0 and carries them into pipe l8, wherein theyare maintained by the steam in a fluidized (entrained stream) state,that is, the coal and steam are so intimately and thoroughly mixed thatthe mixture acts substantially as a flowing gas. Care is required toattain this result, the ratios of coal to steam being held between about0.5 to parts by weight of coal per part of steam. From pipe :0 thefluidized mixture of steam and coal particles is injected into thecoking zone or converter H which is cylindrical in shape and has aconical bottom. Into this converter superheated steam is injected at atemperature between 900 and 1500 C., if the coking is to be conductedunder high temperature carbonization conditions. The superheated steamis injected tangentially so that it swirls about the periphery of theconverter and gradually as it loses heat to the coal particles, spiralsinto the center of the converter, the coal spirals in the same circulardirection but travels from the center of the converter to the; walls.

i'he superheated steam or other heating fluid is introduced into theconverter to supply, preferably, the lowest temperature to the uncokedand the highest temperature to the coked coal. It is known that whencoal is heated to temperatures between 350 and 400 C., it passes throughwhat may be called a plastic or softened state, in which state it isvery sticky and if permitted to do so will stick firmly to mostsurfaces. As the volatile matter is distilled from the coal particles attemperatures above 400 C., the plastic state is passed and the particlesreturn to the solid non-plastic, non-sticky state as coke. Thetangential introduction or" the heating fluid maintains the highesttemperature in the converter on its outer walls and the lowesttemperature in the center. As the coal particles pass from the centeroutwardly, their temperature is raised from inlet temperature throughthe temperatures at which it exists in the plastic state and before theparticles impinge on the walls of the converter they are coked whilepassing through the highest temperature zone of the converter whichexists as a film about its vertical walls. Consequently, the coalparticles when reaching the outer walls of the converter, are in theform of coke which is non-plastic at the temperatures of coking. Thecoal particles, accordingly, fall downwardly and with the gas pass outthe exit 13 from the converter.

As the gases and coke pass from the converter they are quenched by aspray or" water, through pipe lal, which is injected at a sufiicientrate to lower the temperature of the exit stream to in the neighborhoodof 600 C. This is done toprevent decomposition of the ethylene whichoccurs if it is held too long at temperatures substantially above 600 C.The gases and coke pass into the separating zone l5 from the bottom ofwhich the coke is discharged, to a suitable receptacle and all the gasespass through pipe it into a scrubbing tower ll which may be packed withany suitable material such as Raschig rings and wherein water, tars andwater-soluble gases are separated from the other gases present. Theproduced gases are drawn from the scrubber through pipe 18 and treatedfor the separation of the ethylene by any suitable process while thewater-soluble condensable vapor as eilluent passes from the scrubberthrough pipe l9. 7

The apparatus such as is illustrated by the accompanying drawing may beemployed not only for the coking of coal but other carbonaceousmaterials such, for example, as peat, lignite, tar oils, shale, andespecially such highly volatile coals which cake and swell on heating asbituminous, cannel and like coals.

The effect of contact time on the composition of the gas produced isillustrated in Table I. The data from which this table is constructedare based on runs made with Powellton coal ground to a mesh size betweenand and injected with steam at a temperature of 1000 C. into avertically positioned hollow quartz tube having a ratio of length todiameter of approximately 1 to 5.3.

According to the table the maximum ethylene yield occurred with acontact time of 0.33 second, the maximum acetylene yield with a contacttime of 0.49 second and the maximum yield of higher olefins at theminimum contact time, namely, 0.10 second. At lower temperaturessubstantially equivalent results are obtained with somewhat longercontact time.

Other means may be employed than that described in the drawing forpreventing the caking of the powdered coal particles on the walls of thevessel. It may be accomplished by introducing the superheated steam orother carrier gas along the outer walls of the converter by injectingthe steam through a plurality of jets situated at the top and/or bottomof the converter, they being so adapted and arranged that the steamflows parallel to the walls or" the converter and in close proximitythereto. Any other suitable means of introducing the steam so that itacts as a high temperature barrier to the flow of the coal particlestoward the walls may be employed. Internal mixing within the convertermay be provided by suitable baiiies or one or more steam jets may beenclosed within the steam barrier for violent agitation of the particlesin order to insure rapid and uniform heating. The purpose of the steambarrier against the outer wall is identical with its purpose in theconverter illustrated in the drawing, viz. to prevent the partiallycoked coal while in the plastic, sticky state from coming in directcontact with the walls and thereby building up a coke deposit that wouldquickly clog the converter and require shut down of the process forcleaning.

The examples illustrate preferred embodiments of the invention in whichparts are by weight unless otherwise indicated. Examples 1 to 3,inclusive, illustrate operation of the process in equipment somewhatdiiferent from that described by the accompanying drawing, whileExamples 4 to 6, inclusive, were conducted in equipment similar to thatillustrated by the drawing.

Example 1.Carl2onz'eation of powdered cannel coal in steam by radiantheat A West Virginia cannel coal containing 47% volatile matter wasground to 80-150 mesh and fed downward at a rate of 15.8 parts per hourthrough a vertical, tubular silica reaction chamber having a ratio ofdiameter to length of 1 to 5.6. The powdered coke accumulated in thebottom of the vessel while gas was taken off through a side tube nearthe bottom. The converter was externally heated to a temperature ofabout 1000 0., and the time of contact of the powdered coal at thistemperature approximately 0.5 second. The uncondensed gas obtainedcontained 5.65% ethylene plus acetylene and 1.05% higher olefins. Onthis basis the yield of ethylene plus acetylene is 203 lbs. per ton. Thepowdered coke contained 5 volatile matter.

Example 2. Carbonieati0n of powdered bituminous coal in hydrogen byradiant heat Coal from the Powellton seam of West Virginia was groundand sized to 80-150 mesh and was passed downwardly at a rate of 13 partsper hour through a converter along with 21 parts per hour of hydrogen.The converter consisted of a vertical silica tube having a diameter tolength ratio of 1 to 12 and was maintained at a temperature of 900 C. byexternal heating. The coal and hydrogen were admitted into the converterin downward parallel streams. Coke accumulated in the bottom of the tubewhile gas was removed through a side tube near the bottom. The exitgases after removal of tar and coke were passed over activated charcoalat Dry Ice temperature. The gas was regenerated from the charcoal byheating and contained 3.35% ethylene, 0.4% higher olefins, 0.3%acetylene, 2.2% carbon monoxide, 13.4% paraffin hydrocarbons with anaverage molecular weight of about 30; it also contained considerablehydrogen and nitrogen. On this basis the yield of ethylene was lbs. perton and of higher olefins 14 lbs. per ton. The coke contained 6.4%volatile matter.

Example 3.-C'arb0nieati0n of powdered bituminous coal in steam byradiant heat Powellton seam coal (80-150 mesh) described above, waspassed at a rate of 13.4 parts per hour downwardly as a fluidized streamwith 188 parts per hour of dry steam at substantially atmosphericpressure into a vertical, tubular silica converter having a diameter tolength ratio of 1 to 22. The tube was externally heated to a temperatureof 800 C. Upon analysis the gases produced had this composition:

CO2 per cent 0.8 Acetylene do 0.5 Ethylene do 2.4 Higher olefins do 1.0Oxygen do 0.1 Hydrogen do 8.1 Carbon monoxide do 3.5 Parafiins (carbonN0.=1.2) do 7.0 Nitrogen (fed with coal) do 76.6

Yield per ton:

Ethylene pounds 54 Propylene, etc. do 34 Hydrogen-l-CO cu. ft. 3500 Thecoke contained 11.9% volatile matter.

Example 4.Carbonieation of powdered bituminous coal in superheated steamPowellton seam coal (size mesh to dust) was suspended in C. steam (1 lb.coal per 1b. of steam) and passed continuously at a rate of 10 lbs. perhour as a fluidized stream into a reactor having a diameter to length of1 to 2 with a conical bottom and a flat top, the bottom being V again asdeep as the diameter of the reactor. In the reactor the powdered coalwas diluted, heated and coked by steam which had been preheated toapproximately 1020 C. and which was introduced into the converter at arate of 100 lbs/hour, thereby maintaining a reactor temperature of about925 C. The gases and solids passed through the reactor with an averagecontact time of about 0.6 second, after which the mixture leaving thebottom of the reactor was immediately cooled by injection of a smallstream of water to about 600 C. At this temperature powdered'coke wasseparated from the gases in a cyclone separator. The remaining gaseswere further cooled to about 40 C. to condence the carrier steam. Theethylene content of the product gas corresponded to a yield of 40 lbs.ethylene/ton of coal processed.

Example 5.-Powdered Powellton seam coal similar to that used in Examples4 and 5 was fed to the converter at a rate of 12 lbs/hr. The steam tocoal ratio was 17, the reaction temperature 890 C. and the calculatedhold-up time was 0.3 second. The ethylene content of the gas producedcorresponded to a Cal-I4 yield of 53 lbs/ton of coal.

In the specification and attached claims the coal and coke used withsacarrier gas acts like a fluid and is saidto be in a fluidized state;That, state exists'when; the particulate solid has. increased its bulkvolume byat least, 10% due to the flow of gas through; it. As. thevelocityof the gas is increased above this amount up to the velocitythat produces a boiling bed, the state is calledan extended bed, andwhenthe particles have the appearance of a boiling liquid, the state is thatof a boiling bed. Beyond the boiling bed statethe gas and solid moveforward as a stream, which condition'is called an entrained stream. Forpractical utility the entrainedstreamshould contain in..the order of 1pound or more of coal per IOU-cubic feet of gas.

Iclaim:

In a process for the preparation of unsaturated hych'ocarbonsv by thecarbonization of pulverized coal, the; steps which comprise. charging. azone with a static, head of air and pulverized coal, passing thecoal-iromsaid zone by the force of the static head; and by the force ofsteam into a mixing zone to give a thorough intimate-mixture of from 0.5to 30 parts by weight of coal per part of steam, introducing theresulting mixture into the center of a cylindrical coking. zone,injecting steam at a temperature between 7.00 and 1500 C. tangentiallyinto the cylindrical coking zone whereby the super-heated steam swirlsabout the periphery of said cylindrical coking zone and spirals into thecenter ofsaid .zone and whereby the heat for coking the coal flows fromthe circumference of the cylinder toward its axis, thereby preventingthe coal from stick- 3 ing to the cylinder walls while passing; throughthe plastic state, removing the product. gases from the coking zone atsuch a rate that the unsaturated hydrocarbons presentthereinare in thecoking zone for from 0.5 to 3- seconds and immediately after dischargeof the products from the coking zone quenching them with water to atemperature: below 600. C.. the disposition of the coal-steam mixtureand the injection of the high temperature steam into the coking zonebeing so adapted and arranged that coal'and high temperature steam flow.counter-current, the coal from the center toward the walls of the cokingzone, the..steam.from the walls. toward the center of the. coking zone.

AD'ONIRAM J. WELLS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITEDv STATES PATENTS Number Name Date Re. 17,181 McEwen Jan. 1, 19291,432,170 Fenton. Oct. 17, 1922 1,484,258 Fenton Feb. 19, 1924 1,858,834Lucke May 17, 1932 1,950,558 Karrick Mar. 13, 1934 2,337,684 Scheineman1 Dec. 28, 1943 2,406,810 Day Sept. 3, 1946 2,414,586 Eglofi Jan. 21,1947 OTHER REFERENCES Fluidizing Processes, Chemical EngineeringProgress, vol. 43, No.- 8, page 429, August 1947.

Fluidization of Solid Particles, Chemical Engineering'Progress, vol. 44,No. 33, March 1948, page201.

